//
// Created by yewei on 2023/1/4.
//
#include <bits/stdc++.h>

using namespace std;

int main() {
    freopen("../input.txt", "r", stdin);
    string s;
    cin>>s;
    if(s[0]>='0' && s[0]<='9'){
        cout<<"no"<<endl;
        return 0;
    }
    for(int i=0;i<s.length();i++){
        if(s[i]>='0' && s[i]<='9') continue;
        if(s[i]>='a' && s[i]<='z') continue;
        if(s[i]>='A' && s[i]<='Z') continue;
        if(s[i]=='_') continue;
        cout<<"no"<<endl;
        return 0;
    }
    cout<<"yes"<<endl;
}
